The present disclosure generally relates to vehicle suspensions, and more particularly relates to a friction control apparatus for a vehicle suspension.
Friction in vehicle chassis systems can be a positive element helpful for improving vehicle robustness to biased input to the vehicle, such as canted road profile, road disturbance, and asymmetric torque input to the right or left wheels. However, excessive friction can have significant negative influence on the dynamic feel of the vehicle during normal driving and road conditions. The simplest way to add friction to a vehicle chassis system is to apply a high-level friction joint or friction control unit to one or more existing mechanical joints in the chassis. A drawback of this approach is that most of the existing joints in the chassis are particularly designed to deal with significant loads. Manipulating these joints could adversely affect the safety of the vehicle because such manipulation could potentially reduce the loading the joint could otherwise handle.
Two general approaches are conventionally used for applying supplemental friction in a vehicle chassis system. In a first approach, which is a more commonly used approach, mechanical friction in the vehicle chassis system are increased, such as suspension strut bearing frictions and steering gear box friction. Unfortunately, this kind of passive and non-controllable friction degrades with time and, of more concern, causes a downgraded steering feel and vehicle performance.
In a second approach, a controllable supplemental friction is applied to the vehicle chassis system such as to a steering column shaft or a steering rack. Examples of such supplemental controllable friction systems and devices are disclosed in JP 2007-083940, JP 2005-104416, and JP 2000-313349, all expressly incorporated herein by reference. Drawbacks of these prior art supplemental controllable friction systems and devices include requiring major design changes to the vehicle steering or suspension system and corresponding increased costs, significant increased energy usage for such systems and/or degrading the desired smooth and pleasant driving feel of the vehicle.